ANALYTIC STEREOMAPPING USING SPOT IMAGERY
Yubiao Zhong
Research Institute of Surveying & Mapping
16 Beitaiping Road, Beijing 100039
P.R, China
Commission IV
ABSTRACT
Conventional stereophotogrammetric compilation is extended to acquire cartographic
information from SPOT
imagery. À practical approach characterized by a set of improved exterior orientation parameters, which are
updated with time,
Cartesian systems through polynomials is presented.
and fast coordinate transformation between Gauss-Kruger and distortionless
A
(level 1A) is developed on the JX-3 Analytical Plotter,
topographic map and a digital elevation model which has controlled the ZS-1 Orthoprojector to print an
orthophoto, were produced, has proven feasibility of the method.
spatial
software designated to process stereo SPOT images
and an experiment that with images taken in 1986 a
KEY WORDS: Analytical, Polynormial, Photogrammetry, SPOT, Transformation.
INTRODUCTION
Stereophotogrammetric processing of SPOT imagery
using an analytical plotter has been reported in a
number of publications. Because of the complexity
of SPOT imagery geometry and large ground coverage
of each scene, conventional treatments for aerial
frame photographs need to be reformed to fit the
special requirement. Approaches for this purpose
have been established according to different mathe-
matic models, and satisfactory experimental results
were obtained, as presented by Konecny et al.
(1987), Li et al. (1988), and Kratky (1988). In
this paper, a set of improved SPOT imagery orienta-
tion parameters and the fast ground coordinate
transformation, which have been tested with real
image data, are introduced, and the implementation
on the JX-3 Analytical Plotter and ZS-1 Orthopro-
jector manufactured in China is described.
MATHEMATICAL FOUNDATION
In case of aerial frame photography, the only 6 ex-
terior orientation elements of each image of stereo
pair are determined by 3 or more control points,
and thereupon the stereophotogrammetric terrain
model, in which 3-dimensional object coordinates of
a ground point are measured, can be reconstructed.
A SPOT image, however, is characterized by dynamic
scanning, as illustrated in Figure 1. Its exterior
Se te
Orbit
Figure 1. SPOT Imaging and Covered Ground Scene
orientation is variant along the orbital track. In
addition, the ground scene of a SPOT image covers
60 by 60 km rather than 10 by 10 km of a usual aer-
ial photograph with which a map projection coordi-
nate system such as Gauss-Kruger is usually used
directly for photogrammetric processing. A distor-
tion-free rectangular 3-dimensional coordinate
280
system should be selected for processing SPOT
images, and the results are finally converted into
desired map coordinates.
Exterior Orientation Parameters
A SPOT panchromatic image, which is scanned by lin-
early arrayed CCD sensors in continued 9.024 sec-
onds, includes 6000 scanning lines, each of which
is similar geometrically to & frame photograph with
six elements of exterior orientation (the camera
station coordinates Xs, Ys, Zs, and rotation angles
$, Q, K). While an image is being taken, the satel-
lite moves steadily along an elliptic orbit, with
slightly changing flight attitudes. Within an
image, exterior orientations of scanning lines are
highly correlated, and each of the six elements of
a line is expressed as a linear function of time in
most previous treatments. After analyzing the sat-
ellite ephemeris and experimenting with a real
image pair, the quadric polynomial model is intro-
duced here. Table 1 shows the root-mean-square er-
rors (RMSEs) of experimental results, where mS=
4mX? *mY? 4mZ? ,
For SPOT level 1A images, the origin of image coor-
dinates is the scene center, and the y-axis is
defined parallel to scanning direction. Therefore,
six elements of exterior orientation of any scan-
line can be expressed separately as a function of
image ordinate y:
XszXso tk, ytk; y?
Ys=Ys, +k; y+ke v2
Zs-Zso tkeytk, y?
$-6o 4k, ytko y^ (1)
QzQo *ks yk, y?
K=Ko +k, Y+k, y*
where
XSo, YSo, ZSo, to, Ro, and Korepresent the ele-
ments of exterior orientation of center line of
the scene; and ki, ka, ..., kig are linear and
quadric coefficients of variation.
These 18 parameters give the exterior orientation
of a SPOT iamge.
Mutual Transformations between Gauss-Kruger
and Spatial Cartesian Coordinates
Gauss-Kruger projection is used in topographic maps
of 1:500,000 and larger scales in China. A topocen-
tric Cartesian system (TCS) (shown in Figure 2)
whose origin is located at the center of stereopair
overlap is preferably chosen as an object-space
a
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